Method of measuring threshold voltage for a NAND flash memory device
First Claim
1. A method of measuring threshold voltages in a NAND flash memory device including a plurality of cell strings each having a plurality of memory cells connected in series, common drain nodes of the cell strings, common source nodes of the cell strings, wordlines for selecting the memory cells, and a well of a semiconductor substrate in which the memory cell is formed, the method comprising the steps of:
- applying an operation voltage to the well and the common source nodes;
applying a test voltage, which is assigned to measure a threshold voltage, to the wordline of a selected memory cell;
applying a voltage, which is obtained by summing up a pass voltage and the operation voltage, to the wordlines of deselected memory cells;
applying a voltage, which is obtained by summing up a precharge voltage and the operation voltage, to the common drain node; and
detecting a variation of voltage at the common drain node.
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Abstract
Provided is a method of measuring threshold voltages in a NAND flash memory device. In the method, a test voltage is applied to a wordline of selected memory cells to measure a distribution profile of threshold voltages of memory cells. A voltage summing up a pass voltage and an operation voltage is applied to wordlines of deselected cells. The operation voltage is applied to a well and a common source line. A voltage summing up a precharge voltage and the operation voltage is applied to a bitline. After then, a voltage variation on the bitline can be detected to measure a threshold voltage of a memory cell. A negative threshold voltage can be measured by applying a positive voltage with reference to a voltage, as the threshold voltage of the memory cell, set by subtracting the operation voltage from the test voltage in accordance with the bitline voltage variation.
141 Citations
6 Claims
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1. A method of measuring threshold voltages in a NAND flash memory device including a plurality of cell strings each having a plurality of memory cells connected in series, common drain nodes of the cell strings, common source nodes of the cell strings, wordlines for selecting the memory cells, and a well of a semiconductor substrate in which the memory cell is formed, the method comprising the steps of:
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applying an operation voltage to the well and the common source nodes; applying a test voltage, which is assigned to measure a threshold voltage, to the wordline of a selected memory cell; applying a voltage, which is obtained by summing up a pass voltage and the operation voltage, to the wordlines of deselected memory cells; applying a voltage, which is obtained by summing up a precharge voltage and the operation voltage, to the common drain node; and detecting a variation of voltage at the common drain node. - View Dependent Claims (2, 3)
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4. A method of measuring threshold voltages in a NAND flash memory device including a plurality of cell strings each having a plurality of memory cells connected in series, a plurality of bitlines connected to common drain nodes of the cell strings, a common source line connected to common source nodes of the cell strings, wordlines intersecting the bitlines so as to select the memory cells, and a well of a semiconductor substrate in which the memory cell is formed, the method comprising the steps of:
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applying an operation voltage to the well; applying a voltage, which is obtained by summing up a precharge voltage and the operation voltage, to the bitline, applying a test voltage to a selected wordline, applying a voltage, which is obtained by summing up a pass voltage and the operation voltage, to deselected wordlines, and applying the operation voltage to the common source line; and identifying, after detecting a voltage variation of the bitline during a read operation, a threshold voltage of a selected memory cell as a value obtained by subtracting the operation voltage from the test voltage when there is no voltage variation on the bitline, while increasing the test voltage by a predetermined level when the voltage of the bitline decreases. - View Dependent Claims (5, 6)
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Specification